It is known that mono-1-olefins (α-olefins), including ethylene, can be polymerized with catalyst compositions employing titanium, zirconium, vanadium, chromium or other metals, impregnated on a variety of support materials, often in the presence of cocatalysts. These catalyst compositions may be useful for both homopolymerization of ethylene, as well as copolymerization of ethylene with comonomers such as propylene, 1-butene, 1-hexene, or other higher α-olefins. Therefore, there exists a constant search to develop new olefin polymerization catalysts, catalyst activation processes, and methods of making and using catalysts that will provide enhanced catalytic activities and polymeric materials tailored to specific end uses.
One type of catalyst system comprises organometal compounds, particularly metallocene compounds. It is known that contacting water with trimethylaluminum under appropriate conditions forms methyl aluminoxane, and subsequently contacting methyl aluminoxane with a metallocene compound forms a metallocene polymerization catalyst. However, in order to achieve the desired high polymerization activities, large amounts of methyl aluminoxane, and hence large amounts of expensive trimethylaluminum, are necessary to form the active metallocene catalysts. This feature has been an impediment to the commercialization of metallocene catalyst systems, therefore improvements in catalyst compositions and in methods of making the catalyst are needed to afford the desired high polymerization activities.
What are needed are new catalyst compositions and methods of making the catalyst compositions that afford high polymerization activities, and will allow polymer properties to be maintained within the desired specification ranges. One method to achieve this goal is to develop new polymerization methods that provide and utilize catalysts of sufficiently high activity as to be commercially viable.